Electron discharge tube



May 3Q, 1939. H. NICLASSEN ELECTRON DISCHARGE TUBE Filed Oct. 25, 1935 lfi N E R 0 a TL N E R N o M w 1% W H M p/ Patented May 30, 1939 UNl'l'ED STATES ELECTRON DISCHARGE TUBE Hans Niclassen, Berlin, Germany, assignor to N. V. Philips Gloeilampenfabrieken, Eindhoven,

Netherlands Application October 25, 1935, Serial No. 46,714 In Germany October 29, 1934 6 Claims.

My invention relates to electron discharge devices, more particularly to improvements in the envelope therefor.

Walls of electron discharge tubes subjected to an inner or outer pressure above atmospheric pressure should either be made of particularly rigid material or have a particular shape so as to be capable of withstanding the load. This desideratum often prescribes shapes or materials which are detrimental to the treatment of other problems or prevent them from being solved. Thus, for example, the wall must either be fairly well curved or sufficiently thick to withstand the pressures. In the first case, the correspondingly large depth of curvature results in optical distortions. In addition, no plane or substantially plane wall parts can be obtained. In the second case, the discharge tube becomes too heavy or the absorption of the light by the wall becomes too high for some purposes. These problems are particularly important in connection with oscilloscope cathode ray tubes in which there are particular requirements as to the planeness of the luminous screen and the optical quality of the envelope wall. Similarly, it is important for example with photocells that the absorption of the wall for given spectrum bandsbe as small as possible. Similar problems are also important in connection with X-ray tubes or other luminous tubes.

It is possible to obviate the above difliculties in various ways. For example, for the purpose of increasing the ability of withstanding pressures it has been suggested to provide thin tube walls (for example Lenard windows) with riblike or grid-shaped stiffening elements. This solution causes undesirable results such as uneven support shadows on the screen or tube wall and in the difficult manufacture.

It is the principal object of my invention to provide an improved form of envelope for electron discharge tubes particularly of the phototube and cathode ray type and which is light, strong, and while comparatively thin and thus very transparent to light is capable of withstanding high pressures. Another object of my invention is to provide an improved envelope for a cathode ray tube, on the screen of which distortion of the luminous pattern is substantially eliminated.

The idea underlying the present invention is based on the recognition of the fact that the more evenly a given piece of some material is 55 loaded, the higher are the specific loads (pressure or tension per unit weight of material) it is capable of withstanding.

The load of a horizontally mounted rod due. for example, to a weight suspended therefrom always results in breakage at a given point of the material only, that is on the upper side adjacent the supporting point in rupture, on the under side in a comparatively feeble splitting. The recognition of this fact has led in mechanics to the practice of dividing rods or beams thus loaded, in the direction of length into horizontal leaves capable of being displaced relatively to each other.

The present invention is based on a theory similar to this example derived from statics by means of which the load on the walls of electron discharge tubes subjected to inner or outer pressure above atmospheric pressure is relieved. According to the invention, the pressure to which the bulb wall of discharge tubes is subjected is distributed on a plurality of succeeding layers or walls lying in a cascade-like series, so that each wall has to take up only part of the total pressure difference, which may be, for example, one atmosphere. For this purpose the outer wall which is sealed so as to afford a vacuum is divided into two or more layers or successive walls. Each of the compartments formed by these walls is separately exhaustible. It is noted that this term will be used hereinafter to include an increase of the pressure relatively to the open air. For thisreason, the word exhaustible frequently repeated hereinafter is to be understood to mean pumpable in the most general sense of the word. According to the invention, they are exhausted to such a high extent relatively to each other that each successive wall is submitted to less than the highest pressure difference that may occur in the tube.

In this case, the essential direction of the separate divisional layers is not limited to the exact tangential direction. It is true that geometrically the latter is determined in the case of circlecylindrical or other simple shapes, but with more complicated tube sections it cannot be placed on an exact basis, as a determined centre and therefore a radius determined for any point of the surface cannot be indicated. The direction important in this connection is governed by the physical factors, that is by the direction of the increase in pressure. From this it follows that in this case a single direction is without any importance in connection with the progress of the layers, that is the direction of the increase in pressure. Any other direction is more or less suited for the transmission of the gaseous pressure from one layer to the lower one.

Guided by this inventive idea it is important that only a portion of the tube wall, in the case of an X-ray tube for example the window from which the X-rays emerge or with other tubes such as mainly oscilloscope tubes or photocells, particularly the bulb ceiling, should be divided into at least two successive walls each of which is separated from the next one by a cavity or compartment and the pressures existing in the cavities should be such as to constitute, beginning with the outer pressure, a constantly increasing or constantly decreasing series. It may be that for a particular embodiment equally increasing or decreasing series of pressures are not desired and at the beginning or at the end of the series, due to the occurrence of particular conditions, large pressure diiferences or no pressure differences at all may be provided.

The divisional walls which are concave with respect to the inside of the envelope may have either the same depth of curvature or different depths of curvature, inwardly archedwalls being in some cases also suitable. In all of these cases it may be preferable, in view of obtaining the stability of the edge zone, to make the radius of curvature within each individual wall smaller. Similarly, it is possible within the scope of this invention to vary the strength of the walls by the choice of the layer thickness, it being possible in this case to take into account the particular conditions at the edge zone.

The invention can be successfully practised when with the same material and equal thickness of each layer, the pressure differences on both sides of each of the walls is such that for the radius of curvature used the limit of strength is just reached. Any non-observance of this law by increasing the pressure, would result in rupture of the wall thus overloaded. In practice it is always desirable to use a safety factor. In pursuance of this viewpoint the pressure differences are usually made smaller than would be necessary.

By the distribution of the pressure difierence between various successive walls it is possible to decrease the depth of curvature, that is increase the radius of curvature and thus flatten the walls, and yet obtain the strength necessary. Thus the optical path of the rays through the wall of the tube is not materially affected and distortion appears only to a slight extent. It is even possible to make the inner or outer wall substantially plane, which is important in connection with the construction of plane walls, particularly fluorescent screens. I

Besides decreasing the depth of curvature it s, also, possible to reduce the wall thickness of t e material. Thus absorption of the radiations emitted by the tube or becoming operative in it is decreased, which consequently results in an increase in efficiency of such discharge tubes.

By having thicker walls the loaded surface area may be increased, which in many cases offers considerable advantages. Thus, for example, it is possible by proceeding along the lines of this theory materially to increase, for example, with oscilloscope or cathode ray tubes, the surface area of the bulb screen by which the luminous layer is supported. By proceeding along the lines of this theory a similar eifect is obtained with photocells.

In order to prevent persons from being injured by the fragments flying about by a wall breaking for example, and in addition, in order to protect the surface of adjacent walls from being scratched by fragments it may be convenient to coat at least one of the divisional walls, in some cases even several or all of them, with a layer of a substance transparent o rays. For

such, a binding agent of gelatine-like or more When in accordance with the idea underlying theinvention only part of the outer wall of the discharge tube is provided with divisional walls, it may be preferable to make the undivided part of the outer wall of more rigid ma terial, preferably ferrochromium, ceramic material or thick glass. The undivided outer wall which is conductive or made conductive by a metal coating may be connected to earth or to a fixed potential through capacitative or inductive means or a combination of them. The undivided wall part which, for example, may be conical or cylindrical is preferably reinforced at the point of connection to the divisional layers or walls and provided with extension pieces of different heights closed on themselves and matching the peripherial form of the bulb ceiling or end of the envelope or bulb.

Each of the chambers or compartments between the divisional walls is connected to atmosphere by an exhausting channel or duct which can be closed. In this case, the exhausting channels preferably extend wholly or at least partly through the undivided outer wall and they may have outwardly leading conduits or tubes consisting of glass but preferably of metal. These ducts or their outwardly extending tubes can be closed by introducing solder. It is advisable to provide the exhausting conduits with constrictions, particularly pinches, kinks or beads in which the closure is brought about by adherence of the solder.

It may be preferable to introduce into at least one of the compartments formed, one or more substances having at ordinary temperatures a measurable vapor pressure. This offers advantages during exhaustion, as by this means a given vapor pressure independent of the exhausting speed is maintained in the compartment in question. Thus, a control over the vacuum is obtained.

When exhausting the compartments or spaces in which the pressure is to be decreased or increased it is essential that all or part of the spaces to be exhausted shouldbe exhausted substantially at the same time in such manner that the pressure difference to which each individual wall is subjected does not exceed, even for a short time, a limit conforming to this wall. In view of this factor to be taken into account, the spaces should not be exhausted-separately in succession, as thus the pressure difference on both sides of a divisional layer may increase to the extent of exceeding the limit conforming to this layer. Preferably, the spaces to be exhausted simultaneously are connected to a single pump and are exhausted by means of capillary tubes which can be closed separately by taps pressures constitute an increasing series.

or the like and the exhausting resistance of which conforms for each to the pressure to be reached in the particular compartment and to the capacity of the pump. This obviates the need for more than one pump, which otherwise would be necessary for the various spaces to be exhausted. Convenient proportioning of the capillary tubes ensures that although a single pump is used for all of the compartments to be exhausted, these compartments can be exhausted to the pressure that in each individual case is desired.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims, but the invention itself will best be understood by reference to the following description taken in connection with the accompanying drawing in which:

Figure 1 is a diagrammatic .cross section of an electron discharge tube embodying my invention.

Figure 2 is a diagrammatic cross section of another electron discharge tube embodying my invention.

Figure 3 is a view on a larger scale of a portion of the tube shown in Figure 2.

The electron discharge tube shown in Figure 1 is provided in the usual manner with a press It) and an electrode system H carried thereon and the usual base l2. The envelope of the discharge tube comprises,for example, five successive walls l3 and in addition to the inner discharge space M proper has four compartments or chambers which are separated from each other by the walls and each of which can be exhausted separately. On the assumption that the discharge tube is sealed so as to afford a complete vacuum the pressures in the compartments constitute an increasing series such that the compartment closest to the discharge space has only a comparatively small pressure above the complete vacuum existing within the tube and every compartment ly ing further towards the outside has a slightly higher pressure than the adjacent inner compartment or space.

The cathode ray tube or Braun tube in Figure 2 has an end wall or closure member divided into a plurality of successive walls. 3 Thus, for instance, the example of construction comprises three walls lying over each other. The tube is provided with an elongated conical evacuated envelope 2!! having a base 2| and a press 22 supporting an electrode assembly 23. The envelope at its diverging end is provided with a thickened wall 24 to which the successive end walls 25 are sealed as best shown in Figure 3. It will be noticed again, the Thus, just the envelope wall which supports the luminous layer should be as plane as possible and should have a maximum surface area on which the pressure load is not too great. For making the frustoconical wall-body, preferably more rigid material, such as ferrochromium, ceramic material or thick glass, is chosen. This wall part may be connected to ground capacity or inductance or a combination of both or be connected to a fixed potential. At the point of junction, the wall part is preferably reinforced and has a plurality of annular extension pieces which are preferably of different heights and may consist of ferrochromium, even when the wall part per se consists of difierent material. Alternatively, this reinforced uniting thickening may be extended in the form of an individual annular body provided with the annular extension pieces on the wall part and may be subsequently united therewith. This union of the walls with the wall body is shown on a larger scale in Figure 3 in which the extension pieces 26 and 21 of different heights are also clearly shown. These extensions are extended towards the exterior and provide a good union with the glass of the successive walls. Each of the compartments thus formed is separately exhaustible. For this purpose, the thick portion of the envelope provided with the extension pieces may be furnished with exhausting channels or ducts 28 and 30. The exhausting channels are preferably extended by means of outwardly extending tubes 29 and 3| and are provided, either in the exhausting channels themselves or inside the extensions, with a soldering agent 32 which seals the exhaust tubes 29 and 3| subsequent to the. exhausting operation. The exhaust tube is preferably provided at the point to be sealed with a pinch, a kink or a bend in order'that the solder to be liquified by heat may flow together in this constriction and thus seal the tube. The tube of the exhausting channel shown in Figure 2 has sealed to it a small glass tube 32 which in the usual manner is provided with a sealing-off point. The pieces of exhausting tube shown in Figure 3 are intended to be connected to a single exhaust apparatus. For the purpose of dispensing with a plurality of pumps, they may be connected to the same pump via capillary tubes capable of being closed separately by taps or the like; in this case, the exhausting resistance of the capillary tubes should conform to the pressure to be reached in the cavities. The inside of theinnerwall 25 may be coated with fluorescent material 33.

The exhausting operation to which such a multiplex system of compartments is to be subjected and which under other conditions is complicated can be substantially simplified by the employment of this method. The pressure in each space is adjusted automatically and if the capillary tubes are correctly proportioned the control over the individual pressure is unnecessary, once a given exhausting time is determined.

While I have indicated the preferred embodiments of my invention of which I am now aware and have also indicated only one specific. application for which my invention may be employed, it will be apparent that my invention is by no means limited to the exact forms illustrated or the use indicated, but that many variations may be made in the particular structure used and the purpose for which it is employed without departing from the scope. of my invention as set forth in the appended claims.

WhatIclaimasnewis:

1. An electron discharge tube having an elongated evacuated envelope having at one end thereof a plurality of successive walls forming compartments between the walls, said successive walls being curved, the pressure in the compartments increasing from the interior of the envelope to the outside wall, the radius of the cur-v vature of each successive wall being less in advancing from interior to the exterior of the tube and a luminescent coating adjacent the inside surface of the innermost successive wall.

2. An electron discharge tube having an elongated evacuated envelope and provided with an envelope comprising two or more successive walls forming compartments therebetween, one of said walls being provided with a coating of material transparent to light rays and having a characteristic of reducing splintering of the glass when broken and of protecting the surface of adjacent walls from the broken parts of the envelope.

3. An electron discharge tube having an elongatecl evacuated envelope provided at one end with two or more successive walls forming compartments, the pressure in the compartments formed therebetween being such that each individual wall is submitted to less than the highest pressure difierence between the inside and outside of the tube envelope, the inner wall of said successive walls being plane and coated with luminescent material.

4. An electron discharge tube having a conically shaped elongated evacuated envelope having at its diverging end a thickened portion supporting a plurality of concentric extensions of varying height, a plurality of successive walls secured to said extensions for closing the extensions and forming compartments between said walls. 1

5. An electron discharge tube having a conically shaped elongated evacuated envelope having at its diverging end a thickened portion supporting a plurality of concentric extensions of varying height, a plurality of successive walls secured to said extensions for closing the extensions and forming compartments between said walls, each of said compartments being connected to the exterior by means of a duct adapted to be closed when the compartments are exhausted.

6. An electron discharge tube having a conically shaped elongated evacuated envelope having at its diverging end a thickened portion supporting a plurality of concentric extensions of varying height, a plurality of successive walls secured to said extensions for closing the extensions and forming compartments between said walls, each of said compartments being provided with a duct which extends thru the thickened portion of the envelope, said ducts being adapte to be closed.

HANS NICLASSEN. 

